#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv)
{
  int aflag = 0;
  int bflag = 0;
  char *cvalue = NULL;
  int index;
  int c;

  opterr = 0;

  while ((c = getopt(argc, argv, "abc:")) != -1)
    switch (c)
    {
    case 'a':
      aflag = 1;
      break;
    case 'b':
      bflag = 1;
      break;
    case 'c':
      cvalue = optarg;
      break;
    case '?':
      if (optopt == 'c')
        fprintf(stderr, "Option -%c requires an argument.\n", optopt);
      else if (isprint(optopt))
        fprintf(stderr, "Unknown option `-%c'.\n", optopt);
      else
        fprintf(stderr,
                "Unknown option character `\\x%x'.\n",
                optopt);
      return 1;
    default:
      abort();
    }

  printf("aflag = %d, bflag = %d, cvalue = %s\n",
         aflag, bflag, cvalue);

  for (index = optind; index < argc; index++)
    printf("Non-option argument %s\n", argv[index]);
  return 0;
}
/* 
    Here are some examples showing what this program prints with different combinations of arguments:

    % testopt
    aflag = 0, bflag = 0, cvalue = (null)

    % testopt -a -b
    aflag = 1, bflag = 1, cvalue = (null)

    % testopt -ab
    aflag = 1, bflag = 1, cvalue = (null)

    % testopt -c foo
    aflag = 0, bflag = 0, cvalue = foo

    % testopt -cfoo
    aflag = 0, bflag = 0, cvalue = foo

    % testopt arg1
    aflag = 0, bflag = 0, cvalue = (null)
    Non-option argument arg1

    % testopt -a arg1
    aflag = 1, bflag = 0, cvalue = (null)
    Non-option argument arg1

    % testopt -c foo arg1
    aflag = 0, bflag = 0, cvalue = foo
    Non-option argument arg1

    % testopt -a -- -b
    aflag = 1, bflag = 0, cvalue = (null)
    Non-option argument -b

    % testopt -a -
    aflag = 1, bflag = 0, cvalue = (null)
    Non-option argument -
*/